The present invention relates to an airbag module for a motor vehicle.
A driver side airbag module is typically mounted in a motor vehicle""s steering wheel. The module is attached to the hub of the steering wheel and may comprise an airbag, a steering wheel cover, and an inflator. Each of these elements is supported on the steering wheel as known.
To accommodate the location of the airbag, horn switches are frequently placed on the spokes of the steering wheel. A drawback to this particular design is the movement of the horn switch with the rotation of the steering wheel. One design has overcome this problem by incorporating a horn mechanism into the airbag module. This type of horn, called a xe2x80x9cfloating horn,xe2x80x9d is formed by floating the airbag module on a spring assembly within the steering wheel assembly. A horn switch is placed between the airbag module and the base of the steering wheel. To actuate the horn, the entire module is moved toward the steering wheel hub, thereby activating the horn switch and actuating the horn. This horn switch design is expensive and requires a significant gap between the module and the steering wheel so that the module may float.
Another type of horn switch design mounts a thin, flexible membrane switch on the back or inner surface of the steering wheel cover. The membrane switch is spaced between the cover and the folded airbag. Membrane switches conventionally comprise two very thin non-conductive sheets having a conducting coating separated by thin spacers. Pressure on the switch moves the conductive surfaces together to close an electric circuit and actuate the horn.
Membrane switches are expensive and their installation is labor intensive. Moreover, these switches are susceptible to inadvertent actuation, which cause the horn to sound at undesirable times. In particular, when the airbag is not properly folded, pressure is brought to bear on the membrane by the poor folds, thereby resulting in advertent horn actuation. In other instances, extreme hot or cold temperatures can cause the cover to expand or contract, causing the horn to actuate.
A need therefore exists for an airbag module assembly incorporating a horn switch mechanism that avoids the foregoing drawbacks.
The invention comprises an airbag module. The airbag module has an airbag and a cover having a tear seam for the airbag. A backing plate is mounted between the airbag and the cover. Supported between the backing plate and the cover is a horn switch, which sits within a pocket that helps protect the horn switch from inadvertent actuation caused by an airbag fold.
A contact plate between the horn switch and the cover may be employed. The contact plate may be larger than the horn switch to thereby create a larger contact surface area for actuation of the horn switch. The contact plate may have a finger that extends into the pocket of the backing plate to assist in actuation of the horn switch. The contact plate may further be mounted to the backing plate.
The horn switch may comprise two electric contacts, one of which may be mounted to the backing plate. A spring may bias one electric contact away from the other and may also serve to bias the contact plate away from the backing plate. One of the electrical contacts may serve as the spring.
The cover may have two sides, one of which has protrusions in contact with the contact plate to improve horn actuation. The cover may further comprise two portions, divided by the tear seam, with the backing plate mounted to one of the tear portions. In this way, the backing plate will not be ejected during airbag deployment.
The invention may thus employ an inexpensive mechanical horn switch as part of the airbag module. Inadvertent horn actuation is greatly reduced by seating the horn switch around the protective pocket within the backing plate, which further protects the horn switch from the folds of the airbag. In this way, the invention avoids the expense of the membrane switch and insulates the switch from the folds of the airbag. In addition, the airbag module takes up less space than the xe2x80x9cfloating hornxe2x80x9d design.